29. Fungi

Fungi

The Greek root ecto means “outer.” Why are ectomycorrhizal fungi, or EMF, aptly named?
a. Their hyphae form tree-like branching structures inside plant cell walls.
b. They are mutualistic.
c. Their hyphae form dense mats that envelop roots but do not penetrate the cell walls.
d. They transfer nitrogen from outside their plant hosts to the interior.

 No. The mycelium is the feeding network of a fungus. 

 No. The mycelium is the feeding network of a fungus, but it does not store nutrients. 

 No. Fungi "move" to another location through growth of hyphae. But the "movement" is for feeding, which is the specific role of the mycelium. 

Most of the fungal body is given over to this.

In fungi, the function of the mycelium is _____.

Lignin and cellulose provide rigidity to the cell walls of plants. But in most fungi, chitin performs this role. Why is it logical that most fungi don’t have lignin or cellulose in their cell walls?

Fungi feed by                   .
a. producing their own food with the help of sunlight;
b. chasing and capturing other living organisms;
c. growing on their food source and secreting chemicals to break it down;
d. filtering bacteria out of their surroundings;
e. producing spores

 No. Chemoautotrophs get their energy from the breakdown of inorganic chemical compounds. 

 No. Photoautotrophs use sunlight as their energy source. 

 No. Mixotrophs can use both photosynthesis and heterotrophy to obtain energy. 

 No. Photoheterotrophs use light as an energy source but must obtain carbon from organic carbon compounds in the environment. 

What mode of nutrition do fungi use?

Fungi are __________ organisms.

Virtual Reality - Inside a fungal cell

Which of the following cells or structures are associated with asexual reproduction in fungi?
a. ascospores
b. basidiospores
c. zygosporangia
d. conidiophores

 No. Fungi of the phylum Ascomycota produce asexual spores within asci. 

 No. These are structures of fungi and plant roots in a mutualistic relationship. Mycorrhizae are a specialized form of this type of hyphae. 

 No. Basidiocarps are fruiting bodies formed by fungi of the phylum Basidiomycota. 

Review specialized hyphal structures.

Parasitic fungi possess hyphae that are modified to penetrate and absorb nutrients from host tissue. Such modified hyphae are called _____.

 No. Ergots are found on rye. Substances produced by ergots have adverse effects on the human nervous system. 

 No. Truffles can be eaten; the only adverse effect is the impact on your economic condition. 

 No. However, shelf fungi do parasitize weakened and damaged trees. 

 No. However, rust is a destructive plant parasite. 

This is yet another example of an introduced species causing problems in a new environment.

A dramatic example of the pathogenicity of certain fungi is the dramatic decrease of the American chestnut tree by _____.

The mycelial growth habit leads to a body with a high surface-area-to-volume ratio. Why is this important?
a. Mycelia have a large surface area for absorption.
b. The hyphae that make up mycelia are long, thin tubes.
c. Most hyphae are broken up into compartments by walls called septa, although some exist as single, gigantic cells.
d. Hyphae can infiltrate living or dead tissues.

Fungi - 1

The most important adaptive advantage associated with the filamentous nature of fungal mycelia is
a. the ability to form haustoria and parasitize other organisms.
b. the potential to inhabit almost all terrestrial habitats.
c. the increased chance of contact between mating types.
d. an extensive surface area well suited for invasive growth and absorptive nutrition.

 No. Reproductive structures do not make up the bulk of a fungus. 

 No. These are specialized hyphae that enable parasitic fungi to penetrate the tissue of their hosts. 

 No. Pathogenic fungi are usually considerably smaller than this. 

 No. Sporangia are typically aboveground structures and comprise a minor portion of the fungal mass. 

Consider the term that applies to a network of hyphae.

There is a fungus in Oregon that covers 890,965 hectares! The bulk of this fungus is most likely _____.

 mutualistic associations of fungi and plant roots 

 No. Lichens do not consume other organisms. 

 No. Deuteromycetes have no known sexual stage. 

 No. A type of mold is used to produce blue cheese through fermentation. 

 symbiotic associations of photosynthesizers and fungi 

This is another mutualistic relationship in which fungi participate.

Lichens are _____.

 Mycorrhizal fungi prey on nematodes in the soil. 

 No. There are parasitic fungi that prey on nematodes, but they are not mycorrhizal fungi. 

 Mycorrhizal fungi produce carbohydrates needed by plants. 

 No. In fact, the plants supply mycorrhizal fungi with carbohydrates as part of their mutualistic relationship. 

 Mycorrhizal fungi prevent transposons from accumulating in plant cells. 

 No. There is some evidence that some bread molds have genomic defense systems that prevent transposons from accumulating, but this is not part of fungi's mycorrhizal relationship with plants. 

 Mycorrhizal fungi live in plant leaves and produce toxins that discourage herbivores. 

 No. Endophytes are fungi that perform this function. 

 Mycorrhizal fungi assist plants in the absorption of essential nutrients. 

How does the mutualistic relationship between plants and fungi work?

You can buy mycorrhizal fungus to add to soil when you plant trees and other plants. Why would you want to do this?

Cytokinesis

 No. These fungi, known as coenocytic, lack septa. Septa divide hyphae into cells. 

 No. This term describes a mycelium that contains two coexisting, genetically different nuclei. 

 No. This is a term used for fungal species that do not have an identifiable sexual stage. 

 No. This does not describe chytrids, which are known for their zoospores (flagellated spores). 

This is one of the two possible structures of hyphae.

Fungi that consist of a continuous mass containing hundreds or thousands of nuclei are known as _____.

 No. Mycorrhizae are mutualistic associations between fungi and plant roots. 

 No. Opisthokonts form a clade including fungi, animals, and certain protists. 

 No. Basidiomycetes are particularly good at breaking down lignin. 

 No. Some fungi can break down jet fuel, but jet fuel is not a major component of wood. 

Plants need this polymer for strength, but its toughness makes it difficult to decompose.

Fungi in the phylum Basidiomycota are the most important decomposers of wood because of their ability to break down _____.

Explain why fungi that degrade dead plant materials are important to the global carbon cycle. Do you accept the text’s statement that, without these fungi, “Terrestrial environments would be radically different than they are today, and probably much less productive”? Why or why not?

The hyphae of arbuscular mycorrhizal fungi (AMF) form bushy structures after making contact with the plasma membrane of a root cell. What is the function of these structures?
a. They anchor the fungus inside the root, so the association is more permanent.
b. They increase the surface area available for the transfer of nutrients.
c. They produce toxins that protect the plant cells against herbivores.
d. They break down cellulose and lignin in the plant cell wall.

How are fungi different from other organisms?

 an asexual spore-producing structure on a stalk 

 No. Asci are involved in sexual reproduction. 

 a club-shaped cell with spores on its outer surface 

 a cup-shaped structure containing many spore-producing cells on the gill of a mushroom 

 No. Asci are characteristic of Ascomycota. 

 No. It is the sexual structure of ascomycetes. 

This is the basis of the name of a fungal phylum. Recall that fungi are usually grouped according to their sexual stages.

An ascus is _____.

 monokaryotic cells with a haploid nucleus 

 No. One of the listed choices is correct. 

A mushroom is a basidiocarp.

While hiking through a forest, you discover a fungus growing on the remains of a decaying tree trunk. You hypothesize that it is a basidiomycete fungus because it resembles a mushroom in shape and size. If your logic is correct, microscopic analysis of the tissue found in the stalk of this fungus will reveal the presence of _____.

How do fungi live?

Fungi - 2

What does it mean to say that a hypha is dikaryotic?
a. Two nuclei fuse during sexual reproduction to form a zygote.
b. Two independent nuclei, derived from different individuals, are present in each cell.
c. The nucleus is diploid or polyploid—not haploid.
d. It is extremely highly branched, which increases its surface area and thus absorptive capacity.

Introduction to Mycology

All fungi are
a. symbiotic.
b. heterotrophic.
c. flagellated.
d. decomposers.

Comparisons of ribosomal RNA among many different modern species indicate that                   .
a. there are two very divergent groups of prokaryotes;
b. the Protista represents a conglomeration of very unrelated forms;
c. fungi are more closely related to animals than to plants;
d. A and B are correct;
e. A, B, and C are correct

 No. The prefix "di-" does mean "two," but "diploid" refers to having two haploid sets of chromosomes. 

 No. "Multicellular" means having many cells. 

 No. Heterozygosity refers to a genome with two different alleles for a given gene. 

 No. Prokaryotes are organisms that lack a true nucleus. 

Consider the prefix that means "two" and the word for nucleus.

Hyphae with two nuclei per cell are called _____.

 No. Ergots are found on rye, but they can cause serious symptoms if the rye is consumed by humans. Rusts, however, only infect plants. 

 No. Chytrids infect amphibians and are thought to have contributed to the worldwide decline in amphibian stocks. Coccidiodomycosis is a serious mycosis in humans, but it is not especially common. 

Saccharomyces cerevisiae and Penicillium

athlete's foot and Candida (yeast) infections

Think about remedies that you can buy off the shelf in a drugstore.

Two of the most common mycoses (fungal infections) in humans are _____.

Lawns are sometimes fertilized with nitrate that can be washed into neighboring woodlots by rain. If the trees in that woodlot are associated with EMF, what effect might the excess nitrate have on the fungi and/or trees?
a. Fungal growth may be stimulated, causing the trees to transport more nitrogen to the fungi.
b. The fungi may secrete more peptidases to break down the nitrate.
c. The trees may take up the nitrate directly into their roots and rely less on the fungi.
d. The excess nitrate may stimulate the fungi to transport more sugar to the trees.

The closest relatives of fungi are thought to be the
a. animals.
b. vascular plants.
c. mosses.
d. slime molds.

Introduction to Fungus | Microorganisms | Biology | Don't Memorise

You Didn’t Know Mushrooms Could Do All This | National Geographic

This is good old-fashioned evidence.

Evidence that mycorrhizae, the mutualistic relationship between plants and fungi, existed from the beginning of the colonization of land comes from _____.

 No. There is evidence that both fungi and animals evolved from single-celled, aquatic, flagellated protists. 

 No. Note that plants have cellulose in their cell walls and fungi have chitin. 

 No. The evidence does not support this. 

Consider that fungi are heterotrophs.

Molecular evidence suggests that fungi _____.

 No. Parasitic fungi do absorb nutrients from living host organisms, but there is a better answer. 

 No. It is true that mutualistic fungi do absorb nutrients from living host organisms, but there is a better answer. 

 No. Decomposer fungi absorb nutrients from nonliving organic material. 

 All of the listed responses are correct. 

 No. Only the first and second responses are correct.  Decomposer fungi absorb nutrients from nonliving organic material rather than from a living host. 

 The first and second responses are both correct. 

Consider the various symbiotic relationships fungi have with different organisms.

__________ fungi absorb nutrients from living organisms.

 No. Although nearly all glomeromycetes do form mycorrhizae, there is a more specific answer. 

 No. These are the fruiting bodies of ascomycetes. 

 The containment of millions of photosynthetic microorganisms in their hyphae 

 No. These are small clusters of hyphae with embedded algae found in lichens. 

These fungi are of major importance to plants.

What is the major feature of glomeromycetes?

Overview of the Fungal Cell Structure

 No. Lignin is a phytochemical found in the secondary cell walls of plants. 

 No. Cellulose is found in the cell walls of plants. 

 No. Peptidoglycan is unique to the cell walls of bacteria. 

 No. Pectin is a polysaccharide found mostly in the middle lamella of the cell walls of vascular plants. 

This substance is also found in arthropod exoskeletons.

The cell walls of fungal cells are composed of _____.

Many mushrooms are extremely colorful. One hypothesis is that the colors serve as a warning to prevent animals from eating mushrooms, much like the bright yellow and black stripes on wasps help to deter potential predators. Design an experiment to test this hypothesis.

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